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Double cream dilute colors are relatively rare, and as might be expected are found in breeds in which other variants of Cream Dilution occur (palomino, buckskin, smoky black). Examples include the Lusitano, American Saddlebred, Tennessee Walker, Icelandic Horse, Miniature Horse, Paso Fino, Peruvian Paso, Quarter Horse, Welsh Pony, Australian Pony, Shetland Pony, Kinsky, Akhal-Teke, and Byelorussian Harness Horse.
Inheritance of Colors Determined by Cream Dilution
The Cream Dilution mutation is located in the MATP (membrane-associated transporter protein) gene on the twenty-first chromosome. This gene is responsible for the synthesis of a protein, which participates in the process of pigment formation and melanocyte differentiation. This protein is also found in large quantities in melanoma tumor cells.
The mutation of MATP is designated “Ccr,” while the “Wild” allele that does not influence the color of the animal is designated by “C” or “Cr.” The “Ccr” allele is incompletely dominant, and in the heterozygous state it causes dilution of pheomelanin-pigmented regions without an effect on eumelanin colored areas. However, observations show that the regions pigmented with eumelanin also show the action of this gene, although it is not always clearly noticeable. An example can be the brownish coloring of the lower part of the legs in some buckskins, or the brownish shades sometimes encountered in smoky black horses. In some cases the “Ccr” gene in the heterozygous state lightens up the iris color in the eye, which then becomes hazel or amber. A horse homozygous for “Ccr” shows strong pigment dilution not only in the hair, but also in the skin and the iris of the eye (ssss1). The colors caused by Cream Dilution are summarized in Table 3 (see ssss1).